Modular System for Continuous Deposition of a Thin Film Layer on a Substrate

ABSTRACT

A system and associated process for vapor deposition of a thin film layer on a photovoltaic (PV) module substrate is includes establishing a vacuum chamber and introducing the substrates individually into the vacuum chamber. A conveyor system is operably disposed within the vacuum chamber and is configured for conveying the substrates in a serial arrangement through a vapor deposition apparatus within the vacuum chamber at a controlled constant linear speed. A post-heat section is disposed within the vacuum chamber immediately downstream of the vapor deposition apparatus in the conveyance direction of the substrates. The post-heat section is configured to maintain the substrates conveyed from the vapor deposition apparatus in a desired heated temperature profile until the entire substrate has exited the vapor deposition apparatus.

PRIORITY INFORMATION

The present application claims priority to and is a divisional of U.S.patent application Ser. No. 12/638,687 titled “Modular System andProcess for Continuous Deposition of a Thin Film Layer on a Substrate”of Pavol, et al. filed on Dec. 15, 2009, which is incorporated byreference herein.

FIELD OF THE INVENTION

The subject matter disclosed herein relates generally to the field ofthin film deposition processes wherein a thin film layer, such as asemiconductor material layer, is deposited on a substrate. Moreparticularly, the disclosed subject matter is related to a system andprocess for depositing a thin film layer of a photo-reactive material ona glass substrate in the formation of photovoltaic (PV) modules.

BACKGROUND OF THE INVENTION

Thin film photovoltaic (PV) modules (also referred to as “solar panels”or “solar modules”) based on cadmium telluride (CdTe) paired withcadmium sulfide (CdS) as the photo-reactive components are gaining wideacceptance and interest in the industry. CdTe is a semiconductormaterial having characteristics particularly suited for conversion ofsolar energy (sunlight) to electricity. For example, CdTe has an energybandgap of 1.45 eV, which enables it to convert more energy from thesolar spectrum as compared to lower bandgap (1.1 eV) semiconductormaterials historically used in solar cell applications. Also, CdTeconverts energy more efficiently in lower or diffuse light conditions ascompared to the lower bandgap materials and, thus, has a longereffective conversion time over the course of a day or in low-light(e.g., cloudy) conditions as compared to other conventional materials.

Solar energy systems using CdTe PV modules are generally recognized asthe most cost efficient of the commercially available systems in termsof cost per watt of power generated. However, the advantages of CdTe notwithstanding, sustainable commercial exploitation and acceptance ofsolar power as a supplemental or primary source of industrial orresidential power depends on the ability to produce efficient PV moduleson a large scale and in a cost effective manner.

Certain factors affect the efficiency of CdTe PV modules in terms ofcost and power generation capacity of the modules. For example, CdTe isrelatively expensive and, thus, efficient utilization (i.e., minimalwaste) of the material is a primary cost factor. In addition, the energyconversion efficiency of the module is a factor of certaincharacteristics of the deposited CdTe film layer. Non-uniformity ordefects in the film layer can significantly decrease the output of themodule, thereby adding to the cost per unit of power. Also, the abilityto process relatively large substrates on an economically sensiblecommercial scale is a crucial consideration.

CSS (Close Space Sublimation) is a known commercial vapor depositionprocess for production of CdTe modules. Reference is made, for example,to U.S. Pat. No. 6,444,043 and U.S. Pat. No. 6,423,565. Within thedeposition chamber in a CSS process, the substrate is brought to anopposed position at a relatively small distance (i.e., about 2-3 mm)opposite to a CdTe source. The CdTe material sublimes and deposits ontothe surface of the substrate. In the CSS system of U.S. Pat. No.6,444,043 cited above, the CdTe material is in granular form and is heldin a heated receptacle within the vapor deposition chamber. The sublimedmaterial moves through holes in a cover placed over the receptacle anddeposits onto the stationary glass surface, which is held at thesmallest possible distance (1-2 mm) above the cover frame. The cover isheated to a temperature greater than the receptacle.

While there are advantages to the CSS process, the system is inherentlya batch process wherein the glass substrate is indexed into a vapordeposition chamber, held in the chamber for a finite period of time inwhich the film layer is formed, and subsequently indexed out of thechamber. The system is more suited for batch processing of relativelysmall surface area substrates. The process must be periodicallyinterrupted in order to replenish the CdTe source, which is detrimentalto a large scale production process. In addition, the deposition processcannot be readily stopped and restarted in a controlled manner,resulting in significant non-utilization (i.e., waste) of the CdTematerial during the indexing of the substrates into and out of thechamber, and during any steps needed to position the substrate withinthe chamber.

Accordingly, there exists an ongoing need in the industry for animproved system and method for economically feasible large scaleproduction of efficient PV modules, particularly CdTe based modules.

BRIEF DESCRIPTION OF THE INVENTION

Aspects and advantages of the invention will be set forth in part in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

In accordance with an embodiment of the invention, a process is providedfor vapor deposition of a thin film layer, such as a CdTe layer, on aphotovoltaic (PV) module substrate. A “thin” film layer is generallyrecognized in the art as less than 10 microns (μm), although theinvention is not limited to any particular film thickness. The processincludes conveying substrates in serial arrangement through a vapordeposition apparatus in a vacuum chamber wherein a thin film of asublimed source material is deposited onto an upper surface of thesubstrates. The substrates are conveyed through the vapor depositionapparatus at a controlled constant linear speed such that leading andtrailing sections of the substrates in a conveyance direction areexposed to the same vapor deposition conditions within the vapordeposition apparatus. The substrates are post-heated as they areconveyed out of the vapor deposition apparatus such that a substantiallyuniform temperature profile is maintained along the length of thesubstrates until the entire substrate is conveyed out of the vapordeposition apparatus. The substrates are then controllably cooled beforebeing removed from the vacuum chamber.

In an alternate process embodiment, the substrates are post-heated asthey are conveyed out of the vapor deposition apparatus in a manner suchthat a controlled gradually decreasing temperature gradient isestablished along the length of the substrates until the entiresubstrate is conveyed out of the vapor deposition apparatus. Thedecreasing temperature gradient is of a nature such that damage to thesubstrate, such as warping, breaking, and so forth, is prevented.

Variations and modifications to the processes discussed above are withinthe scope and spirit of the invention and may be further describedherein. In accordance with another embodiment of the present invention,a system is provided for vapor deposition of a thin film layer, such asa CdTe film layer, on photovoltaic (PV) module substrates. The systemincludes a vacuum chamber, which may be defined by a plurality ofinterconnected modules in a particular embodiment. The vacuum chamberincludes a vapor deposition apparatus configured for depositing a thinfilm of a sublimed source material onto an upper surface of substratesconveyed therethrough. A conveyor system is operably disposed within thevacuum chamber and is configured for conveying the substrates in aserial arrangement through the vapor deposition apparatus at acontrolled constant linear speed. A post-heat section is disposed withinsaid vacuum chamber immediately downstream of the vapor depositionapparatus in the conveyance direction of the substrates. The post-heatsection is configured to maintain the substrates conveyed from the vapordeposition apparatus at a desired heated temperature profile thatprevents thermal damage to the substrates until the entire substrate hasexited the vapor deposition apparatus. The post-heat section may includeone or more post-heat modules having controllable heat zones

In a particular embodiment, the post-heat section is configured to heatthe substrates such that a substantially uniform temperature profile ismaintained along the length of the substrates until the entire substrateis conveyed out of said vapor deposition apparatus.

In an alternate embodiment, the post-heat section is configured to heatthe substrates in a manner such that a controlled gradually decreasingtemperature gradient profile is established along the length of thesubstrates until the entire substrate is conveyed out of the vapordeposition apparatus.

Variations and modifications to the embodiments of the system assemblydiscussed above are within the scope and spirit of the invention and maybe further described herein.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims.

BRIEF DESCRIPTION OF THE DRAWING

A full and enabling disclosure of the present invention, including thebest mode thereof, is set forth in the specification, which makesreference to the appended drawings, in which:

FIG. 1 is a plan view of an embodiment of a system in accordance withaspects of the invention; and,

FIG. 2 is a perspective view of the embodiment of the system of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made in detail to embodiments of the invention,one or more examples of which are illustrated in the drawings. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations can be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment, can be used with another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventionencompass such modifications and variations as come within the scope ofthe appended claims and their equivalents.

FIGS. 1 and 2 illustrate an embodiment of a system 10 configured forvapor deposition of a thin film layer on a photovoltaic (PV) modulesubstrate 14 (referred to hereafter as a “substrate”). The thin film maybe, for example, a film layer of cadmium telluride (CdTe). Although theinvention is not limited to any particular film thickness, as mentioned,it is generally recognized in the art that a “thin” film layer on a PVmodule substrate is generally less than about 10 microns (μm). It shouldbe appreciated that the present system is not limited to vapordeposition of a particular type of film layer, and that CdTe is just onetype of film layer that may be deposited by the system 10.

Referring to FIG. 1, the system 10 includes a vacuum chamber 16, whichmay be defined by any configuration of components. In the particularillustrated embodiment, the vacuum chamber 16 is defined by a pluralityof interconnected modules, as discussed in greater detail below. Ingeneral, the vacuum chamber 16 may be considered as the section orportion of the system 10 wherein a vacuum is drawn and maintained forthe various aspects of the vapor deposition process.

The system 10 includes a preheat section 18 within the vacuum chamber16. The preheat section 18 may be one or a plurality of components thatpreheat the substrates 14 as they are conveyed through the vacuumchamber 16. In the illustrated embodiment, the preheat section 18 isdefined by a plurality of interconnected modules 20 through which thesubstrates 14 are conveyed.

The vacuum chamber 16 also includes a vapor deposition apparatus 24downstream of the preheat section 18 in the direction of conveyance ofthe substrates 14. This apparatus 24 may be configured as a vapordeposition module 22 and is the component configuration wherein a sourcematerial, such as granular CdTe material, is sublimated and depositedonto the substrate 14 as a thin film layer. It should be readilyappreciated that various vapor deposition systems and processes areknown in the art, such as the CSS systems discussed above, and that thevapor deposition apparatus 24 is not limited to any particular type ofvapor deposition system or process.

The vacuum chamber 16 also includes a cool-down section 26 downstream ofthe vapor deposition apparatus 24. In the illustrated embodiment, thecool-down section 26 is defined by a plurality of interconnectedcool-down modules 28 through which the substrates 14 are conveyed priorto being removed from the system 10, as described in greater detailbelow.

The system 10 also includes a conveyor system that is operably disposedwithin the vacuum chamber 16. In the illustrated embodiment, thisconveyor system 16 includes a plurality of individual conveyors 66, witheach of the modules in the system 10 including a respective one of theconveyors 66. It should be appreciated that the type or configuration ofthe conveyors 66 is not a limiting factor of the invention. In theillustrated embodiment, the conveyors 66 are roller conveyors driven bya motor drive 67 (FIG. 2) that is controlled so as to achieve a desiredconveyance rate of the substrates 14 through a respective module, andthe system 10 overall.

The system 10 also includes a feed system 48 (FIG. 2) that is configuredwith the vapor deposition apparatus 24 to supply the apparatus 24 withsource material, such as granular CdTe material. The feed system 48 maytake on various configurations within the scope and spirit of theinvention, and functions so as to supply the source material withoutinterrupting the continuous vapor deposition process within the vapordeposition apparatus 24 or conveyance of the substrates 14 through thevapor deposition apparatus 24.

Referring to FIGS. 1 and 2 in general, the individual substrates 14 areinitially placed onto a load conveyor 46, which may include, forexample, the same type of driven roller conveyor 66 that is utilized inthe other system modules. The substrates 14 are first conveyed throughan entry vacuum lock station 34 that is upstream of the vacuum chamber16. In the illustrated embodiment, the vacuum lock station 34 includes aload module 36 upstream of a buffer module 38 in the direction ofconveyance of the substrates 14. A “rough” (i.e., initial) vacuum pump56 is configured with the load module 36 to drawn an initial vacuumlevel, and a “fine” (i.e., high) vacuum pump 58 is configured with thebuffer module 38 to increase the vacuum in the buffer module 38 toessentially the vacuum level within the vacuum chamber 16. Valves 62(e.g., gate-type slit valves or rotary-type flapper valves) are operablydisposed between the load conveyor 46 and the load module 36, betweenthe load module 36 and the buffer module 38, and between the buffermodule 38 and the vacuum chamber 16. These valves 62 are sequentiallyactuated by a motor or other type of actuating mechanism 64 in order tointroduce the substrates 14 into the vacuum chamber 16 in a step-wisemanner without adversely affecting the vacuum within the chamber 16.

Under normal operating conditions, an operational vacuum is maintainedin the vacuum chamber 16 by way of any combination of vacuum pumps 58,56, and 60. In order to introduce a substrate 14 into the vacuum chamber16, the valve 62 between the load module 36 and buffer module 38 isinitially closed and the load module is vented. The valve 62 between thebuffer module 38 and first pre-heat module 20 is closed. The valve 62between the load module 36 and load conveyor 46 is opened and theindividual conveyors 66 in the respective modules are controlled so asto advance a substrate 14 into the load module 36. At this point, thefirst valve 62 is shut and the substrate 14 is isolated in the loadmodule 36. The rough vacuum pump 56 then draws an initial vacuum in theload module 36. During this time, the fine vacuum pump 58 draws a vacuumin the buffer module 38. When the vacuum between the load module 36 andbuffer module 38 are substantially equalized, the valve 62 between themodules is opened and the substrate 14 is moved into the buffer module38. The valve 62 between the modules is closed and the fine vacuum pump58 increases the vacuum in the buffer module 38 until it issubstantially equalized with the adjacent pre-heat module 20. The valve62 between the buffer module 38 and pre-heat module 20 is then openedand the substrate is moved into the pre-heat module 20. This processrepeats for each substrate 14 conveyed into the vacuum chamber 16.

In the illustrated embodiment, the preheat section 18 is defined by aplurality of interconnected modules 20 that define a heated conveyancepath for the substrates 14 through the vacuum chamber 16. Each of themodules 20 may include a plurality of independently controlled heaters21, with the heaters 21 defining a plurality of different heat zones. Aparticular heat zone may include more than one heater 21.

Each of the preheat modules 20 also includes an independently controlledconveyor 66. The heaters 21 and conveyors 66 are controlled for eachmodule 20 so as to achieve a conveyance rate of the substrates 14through the preheat section 18 that ensures a desired temperature of thesubstrates 14 prior to conveyance of the substrates 14 into a downstreamvapor deposition module 22.

In the illustrated embodiment, the vapor deposition apparatus 24includes a module 22 in which the substrates 14 are exposed to a vapordeposition environment wherein a thin film of sublimed source material,such as CdTe, is deposited onto the upper surface of the substrates 14.The individual substrates 14 are conveyed through the vapor depositionmodule 22 at a controlled constant linear speed. In other words, thesubstrates 14 are not stopped or held within the module 24, but movecontinuously through the module 22 at a controlled linear rate. Theconveyance rate of the substrates 14 may be in the range of, forexample, about 10 mm/sec to about 40 mm/sec. In a particular embodiment,this rate may be, for example, about 20 mm/sec. In this manner, theleading and trailing sections of the substrates 14 in the conveyancedirection are exposed to the same vapor deposition conditions within thevapor deposition module 22. All regions of the top surface of thesubstrates 14 are exposed to the same vapor conditions so as to achievea substantially uniform thickness of the thin film layer of sublimatedsource material on the upper surface of the substrates 14.

The vapor deposition module 22 includes a respective conveyor 65, whichmay be different from the conveyors 66 in the plurality of upstream anddownstream modules. Conveyor 65 may be particularly configured tosupport the vapor deposition process within the module 22. In theembodiment illustrated, an endless slat conveyor 65 is configured withinthe module 22 for this purpose. It should be readily appreciated,however, that any other type of suitable conveyor may also be used.

The vapor deposition apparatus 24 is configured with a feed system 48(FIG. 2) to continuously supply the apparatus 24 with source material ina manner so as not to interrupt the vapor deposition process or non-stopconveyance of the substrates 14 through the module 22. The feed system48 is not a limiting factor of the invention, and any suitable feedsystem 48 may be devised to supply the source material into the module22. For example, the feed system 48 may include sequentially operatedvacuum locks wherein an external source of the material is introduced asmetered doses in a step-wise manner through the vacuum locks and into areceptacle within the vapor deposition apparatus 24. The supply ofsource material is considered “continuous” in that the vapor depositionprocess need not be stopped or halted in order to re-supply theapparatus 24 with source material. So long as the external supply ismaintained, the feed system 48 will continuously supply batches ormetered doses of the material into the vapor deposition apparatus 24.

In the illustrated embodiment, a post-heat section 30 is defined withinthe vacuum chamber 16 immediately downstream of the vapor depositionmodule 22. This post-heat section 30 may be defined by one or morepost-heat modules 32 having a heater unit 21 configured therewith. Theheat unit 21 may include multiple independently controlled heat zones,with each zone having one or more heaters. As the leading section of asubstrate 14 is conveyed out of the vapor deposition module 24, it movesinto the post-heat module 32. The post-heat module 32 maintains acontrolled heating profile of the substrate until the entire substrateis moved out of the vapor deposition module 22 to prevent damage to thesubstrate, such as warping or breaking caused by uncontrolled or drasticthermal stresses. If the leading section of the substrate 14 wereallowed to cool at an excessive rate as it exited the module 22, apotentially damaging temperature gradient would be generatedlongitudinally along the substrate 14. This condition could result inthe substrate breaking from thermal stress.

In a particular embodiment, the post-heat section 16 is controlled toestablish a substantially uniform or constant temperature throughout thesection 16. For example, in the embodiment wherein the post-heat section16 includes a module 324 and heater unit 21, the heater unit maintains aconstant temperature along the longitudinal dimension of the module 32.In this configuration, a substantially uniform temperature profile isgenerated in the substrates 14 as they are conveyed out of the vapordeposition apparatus 24 and through the post-heat module 32 until theentire substrate 14 is conveyed out of the vapor deposition apparatus24.

In the embodiment wherein the substrates are maintained at a uniformtemperature profile through the post-heat module 32, the substrates maybe conveyed at a first conveyance rate into the module 32, and conveyedfrom the post-heat module 32 into an adjacent cool-down section 26(e.g., into a first cool-down module 28) at a substantially greatersecond conveyance rate that is effective to prevent a thermal gradientfrom being established along the length of the substrates 14. In otherwords, the substrates 14 are moved into the cool-down section 26 as sucha rate that a damaging thermal gradient cannot be established along thelength of the substrate. In essence, the entire substrate 14 issubjected to the cooling conditions at essentially the same time so thatthermal stresses are not induced in the substrate material. Inparticular embodiments, the first conveyance rate is from about 10mm/sec to about 40 mm/sec, and the second conveyance rate is from about200 mm/sec to about 600 mm/sec. The substrates 14 may then be conveyedthrough the cool-down section 26 at about the first conveyance rate.

In an alternate embodiment related to the post-heat process, thepost-heat section (e.g., post-heat module 32) is controlled in a mannersuch that a controlled gradually decreasing temperature gradient profileis established along the length of the substrates 14 until the entiresubstrate is conveyed out of the vapor deposition apparatus 24. In otherwords, the leading section of the substrate 14 will have a decreasedtemperature as compared to the trailing section of the substrate as thesubstrate moves through the module 32. This decreasing temperaturegradient is carefully controlled so that an excessive and potentiallydamaging gradient is not established. It should be appreciated that thesubstrates 14 can endure some degree of a thermal gradient without beingdamaged, and this particular embodiment takes advantage of thischaracteristic by allowing some initial cooling of the leading sectionof the substrate 14. This embodiment allows for the substrates 14 to beconveyed through the vapor deposition apparatus 24, into and through thepost-heat module 32, and into and through the cool-down section 26 atsubstantially the same constant liner speed.

The gradually decreasing temperature gradient for the substrates 14discussed above may be accomplished by maintaining a temperature profilealong the length of the post-heat section of about 400 degrees C. toabout 600 degrees C. at an inlet thereof and about 200 degrees C. toabout 500 degrees C. at an outlet thereof. Individual heating zoneswithin the post-heat section 26 may be controlled to establish thisprofile in a linear or step-wise manner along the length of thepost-heat section 26.

As referenced above, a cool-down section 26 is downstream of thepost-heat section 30 within the vacuum chamber 16. The cool-down section26 may include one or more cool-down modules 28 having independentlycontrolled conveyors 66. The cool-down modules 28 define alongitudinally extending section within the vacuum chamber 16 in whichthe substrates having the thin film of sublimed source materialdeposited thereon are allowed to cool at a controlled cool-down rateprior to the substrates 14 being removed from the system 10. Each of themodules 28 may include a forced cooling system wherein a cooling medium,such as chilled water, refrigerant, or other medium is pumped throughcooling coils 29 configured with the modules 28, as particularlyillustrated in FIG. 2.

An exit vacuum lock station 40 is configured downstream of the cool-downsection 26. This exit station 40 operates essentially in reverse of theentry vacuum lock station 34 described above. For example, the exitvacuum lock station 40 may include an exit buffer module 42 and adownstream exit lock module 44. Sequentially operated valves 62 aredisposed between the buffer module 42 and the last one of the modules 28in the cool-down section 26, between the exit buffer module 42 and theexit lock module 44, and between the exit lock module 44 and an exitconveyor 50. A fine vacuum pump 58 is configured with the exit buffermodule 42, and a rough vacuum pump 56 is configured with the exit lockmodule 44. The pumps 58, 60, and valves 62 are sequentially operated(essentially in reverse of the entry lock station 34) to move thesubstrates 14 out of the vacuum chamber 16 in a step-wise fashionwithout loss of vacuum condition within the vacuum chamber 16.

As mentioned, in the embodiment illustrated, the system 10 is defined bya plurality of interconnected modules, with each of the modules servinga particular function. For example, modules 36 and 38 function tointroduce individual substrates 14 into the vacuum chamber 16. Theconveyors 66 configured with these respective modules are appropriatelycontrolled for this purpose, as well as the valves 62 and associatedactuators 64. The conveyors 66 and heater units 21 associated with theplurality of modules 20 in the pre-heat section 18 are controlled topre-heat the substrates 14 to a desired temperature, as well as toensure that the substrates 14 are introduced into the vapor depositionmodule 22 at the desired controlled, constant linear conveyance rate.For control purposes, each of the individual modules may have anassociated independent controller 52 configured therewith to control theindividual functions of the respective module. The plurality ofcontrollers 52 may, in turn, be in communication with a central systemcontroller 54, as illustrated in FIG. 1. The central system controller54 can monitor and control (via the independent controllers 52) thefunctions of any one of the modules so as to achieve an overall desiredconveyance rate and processing of the substrates 14 through the system10.

Referring to FIG. 1, for independent control of the individualrespective conveyor 66, each of the modules may include any manner ofactive or passive sensors 68 that detect the presence of the substrates14 as they are conveyed through the module. The sensors 68 are incommunication with the module controller 52, which is in turn incommunication with the central controller 54. In this manner, theindividual respective conveyor 66 may be controlled to ensure that aproper spacing between the substrates 14 is maintained and that thesubstrates 14 are conveyed at the desired constant conveyance ratethrough the vacuum chamber 16.

The present invention also encompasses various process embodiments forvapor deposition of a thin film layer on a photovoltaic (PV) modulesubstrate. The processes may be practiced with the various systemembodiments described above or by any other configuration of suitablesystem components. It should thus be appreciated that the processembodiments according to the invention are not limited to the systemconfiguration described herein.

In a particular embodiment, the process includes establishing a vaporchamber and introducing PV substrates individually into the chamber. Thesubstrates are preheated to a desired temperature as they are conveyedthrough the vacuum chamber in a serial arrangement. The preheatedsubstrates are then conveyed through a vapor deposition apparatus withinthe vacuum chamber wherein a thin film of a sublimated source material,such as CdTe, is deposited onto the upper surface of the substrates. Thesubstrates are conveyed through the vapor deposition apparatus at acontrolled constant linear speed such that the leading and trailingsections of the substrates in a conveyance direction are exposed to thesame vapor deposition conditions within the vapor deposition apparatusso as to achieve a uniform thickness of the thin film layer on the uppersurface of the substrates.

In a unique embodiment, the vapor deposition apparatus is supplied withsource material in a manner so as not to interrupt the vapor depositionprocess or conveyance of the substrates through the vapor depositionapparatus.

The process may further include cooling the substrates downstream of thevapor deposition apparatus within the vacuum chamber prior to subsequentremoval of each of the cooled substrates from the vacuum chamber.

It may be desired to post-heat the substrates as they exit the vapordeposition apparatus prior to cooling the substrates such that theleading section of the substrates in the direction of conveyance is notcooled until the entire substrate has exited the vapor depositionapparatus. In this manner, the substrate is kept at a relativelyconstant temperature along its longitudinal length while the trailingsection of the substrate is undergoing the deposition process within thevapor deposition apparatus.

As mentioned, the substrates are conveyed through the vapor depositionapparatus at a constant linear speed. In a unique embodiment, thesubstrates may be conveyed through the other sections of the vacuumchamber at a variable speed. For example, the substrates may be conveyedat a slower or faster speed, or step-wise, as they are pre-heated beforethe vapor deposition apparatus, or as they are cooled after the vapordeposition apparatus.

The process may also include individually introducing the substratesinto and out of the vacuum chamber through an entry and exit vacuum lockprocess wherein the vacuum conditions within the vacuum chamber are notinterrupted or changed to any significant degree.

In order to sustain a continuous vapor deposition process, the processalso may include supplying the source material to the vapor depositionapparatus from an externally refillable feed system. The feed processmay include continuously introducing metered doses of the sourcematerial from the feed system into the vapor deposition apparatuswithout interrupting the vapor deposition process. For example, themetered doses of source material may be introduced through sequentialvacuum locks and deposited into a receptacle within the vapor depositionapparatus. In this manner, the vapor deposition process need not beinterrupted to refill the source material within the vapor depositionapparatus.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed is:
 1. A system for vapor deposition of a thin filmlayer on photovoltaic (PV) module substrates, comprising: a vacuumchamber, said vacuum chamber further comprising a vapor depositionapparatus configured for depositing a thin film of a sublimed sourcematerial onto an upper surface of substrates conveyed therethrough; aconveyor system operably disposed within said vacuum chamber andconfigured for conveying the substrates in a serial arrangement throughsaid vapor deposition apparatus at a controlled constant linear speed;and, a post-heat section disposed within said vacuum chamber immediatelydownstream of said vapor deposition apparatus in the conveyancedirection of the substrates, said post-heat section configured tomaintain the substrates conveyed from said vapor deposition apparatus ina desired heated temperature profile until the entire substrate hasexited said vapor deposition apparatus.
 2. The apparatus as in claim 1,wherein said post-heat section is configured to heat the substrates witha temperature profile such that a substantially uniform temperature ismaintained along the length of the substrates until the entire substrateis conveyed out of said vapor deposition apparatus.
 3. The apparatus asin claim 2, further comprising a cool-down section downstream of saidpost-heat section in a direction of conveyance of the substrates, saidconveyor system configured to convey the substrates through said vapordeposition apparatus and into said post-heat section at a firstconveyance rate, and from said post-heat section and into said cool-downsection at a substantially greater second conveyance rate effective toprevent a thermal gradient from being established along the length ofthe substrates.
 4. The apparatus as in claim 3, wherein the firstconveyance rate is from about 10 mm/sec to about 40 mm/sec, and thesecond conveyance rate is from about 200 mm/sec to about 600 mm/sec. 5.The apparatus as in claim 1, wherein said post-heat section isconfigured to heat the substrates with a temperature profile such that acontrolled gradually decreasing temperature gradient is establishedalong the length of the substrates until the entire substrate isconveyed out of said vapor deposition apparatus.
 6. The apparatus as inclaim 5, wherein said post-heat section comprises a module havingseparately controlled heating zones, and wherein said post-heat moduleis maintainable at a temperature of from about 400 degrees C. to about600 degrees C. at an inlet thereof and decreasing to about 200 degreesC. to about 500 degrees C. at an outlet thereof.
 7. The apparatus as inclaim 5, further comprising a cool-down section downstream of saidpost-heat module in a direction of conveyance of the substrates, saidconveyor system configured to convey the substrates through said vapordeposition apparatus, into and through the post-heat module, and intoand through the cool-down section at substantially the same constantliner speed.